Sens. Angus King (I-Maine) and Roger Wicker (R-Miss.) announced on Thursday that they had both tested positive for the coronavirius—marking two breakthrough cases for the Senate this week. 

The senators, who announced their cases separately within hours of each other, are both fully vaccinated. The Senate left town last week and isn't scheduled to return until mid-September.  

King, in his statement, said that while he and his staff took precautions to social distance while in Washington. D.C., that he began "feeling mildly feverish" on Wednesday and got tested in Maine on Thursday. 

"It came back positive.  While I am not feeling great, I’m definitely feeling much better than I would have without the vaccine. I am taking this diagnosis very seriously, quarantining myself at home and telling the few people I’ve been in contact with to get tested in order to limit any further spread," King said in a statement.

Phillip Waller, a spokesperson for Wicker, added that the Mississippi Republican tested positive on Thursday, and that he got tested because he was experiencing "mild symptoms." 

"Senator Wicker is fully vaccinated against COVID-19, is in good health, and is being treated by his Tupelo-based physician. He is isolating, and everyone with whom Senator Wicker has come in close contact recently has been notified," he said. 

The back-to-back announcements from Wicker and King make them the second and third known breakthrough cases — when a fully vaccinated individual tests positive — in the Senate.

Sen. Lindsey Graham (R-S.C.) became the first known breakthrough case amongst senators earlier this month, when he announced that he had tested positive. Graham quarantined and returned to the Senate last week in time to vote on a budget blueprint for Democrats' $3.5 trillion spending plan.

Public health officials have stressed that symptomatic breakthrough infections for fully vaccinated individuals are rare and getting vaccinated makes getting a severe case of the coronavirus less likely. 

A CNN survey earlier this year found that at least 96 of 100 senators had been vaccinated. Testing is also available within the Capitol complex. 

But senators are now spread out across the country for the summer break, with the number of total daily new cases in the United States climbing in recent weeks but still significantly below peaks reached late last year and in early January. 

Mississippi, where 36 percent of the total population is fully vaccinated, has seen a 91 percent increase in its number of cases over the past 14 days and has an average of 3,526 cases per day, according to New York Times data.

Maine, where 65 percent of the total population is fully vaccinated, has seen 71 percent increase in its number of cases over the past 14 days with an average of 172 cases per day, according to Times data.

King, in his statement, urged unvaccinated individuals to get vaccinated. According to data from the Centers for Disease Control and Prevention (CDC), less than 1 percent of fully vaccinated Americans have had a breakthrough case that results in hospitalization or death.

“I will keep everyone posted in the days ahead of the healing process, but I urge everyone to remain vigilant, follow the guidance from health professionals, and get vaccinated if you haven’t been," he said.

—Updated at 2:25 p.m.